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* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. 1) The smallest stable units of matter are 1) _______ A) electrons. B) molecules. C) protons. D) neutrons. E) atoms. 2) The "atomic number" of an atom is determined by the number of ________ it has. A) protons + neutrons B) protons C) electrons D) protons + electrons E) neutrons 2) _______ 3) Isotopes of an element differ in the number of A) electron clouds. B) protons in the nucleus. C) electrons in energy shells. D) electrons in the nucleus. E) neutrons in the nucleus. 3) _______ 4) The mass number represents the number of A) neutrons in an atom. B) protons in an atom. C) neutrons + electrons. D) electrons in an ion. E) protons + neutrons. 4) _______ 5) The "atomic weight" of an atom reflects the average number of A) protons + neutrons. B) protons. C) protons + neutrons + electrons. D) neutrons. E) electrons. 5) _______ 6) Radioisotopes have unstable A) electron clouds. B) nuclei. C) protons. D) ions. E) isotopes. 6) _______ 7) The chemical behavior of an atom is determined by A) the outermost electron shell. B) the mass of the nucleus. C) the number of neutrons. D) the number of protons. E) the size of the atom. 7) _______ 8) Ions with a + charge are called A) anions. B) positrons. C) isotopes. D) cations. E) radicals. 8) _______ 9) The nucleus of an atom consists of A) electrons. B) protons. C) protons + neutrons. D) protons + electrons. E) neutrons. 9) _______ 10) By weight, which element is the most plentiful in the human body? A) oxygen B) carbon C) sodium D) potassium E) sulfur 10) ______ 11) By weight, which element is the second most abundant in the human body? A) carbon B) oxygen C) hydrogen D) nitrogen E) calcium 11) ______ 12) The innermost electron shell in an atom holds up to ________ electrons. A) 2 B) 1 C) 8 D) 6 E) 4 12) ______ 13) Indicate which of these lists contains only trace elements. A) sulfur, chlorine, oxygen B) boron, oxygen, carbon C) selenium, hydrogen, calcium D) cobalt, calcium, sodium E) silicon, fluorine, tin 13) ______ 14) The mass of an atom is largely determined by the number of ________ it has. A) electrons B) protons + neutrons C) protons D) protons + electrons E) neutrons 14) ______ 15) A nanometer is A) 10-9 meter. 15) ______ B) 10-10 meter. C) 10-12 meter. D) 10-6 meter. E) 10-8 meter. 16) If an isotope of oxygen has 8 protons, 10 neutrons, and 8 electrons, its mass number is A) 12. B) 26. C) 18. D) 8. E) 16. 16) ______ 17) Which element commonly has only a proton as its nucleus? A) neon B) helium C) argon D) hydrogen E) none of the above 17) ______ 18) If an element is composed of atoms with an atomic number of 6 and a mass number of 14, then a neutral atom of this element contains A) 8 electrons. B) 6 protons. C) 8 neutrons. D) both A and B E) both A and C 18) ______ 19) In a molecule of nitrogen, three pairs of electrons are shared by two nitrogen atoms. The type of bond that is formed is an example of a(n) A) single trivalent bond. B) double divalent bond. C) triple covalent bond. D) hydrogen bond. E) polar covalent bond. 19) ______ 20) If a pair of electrons is unequally shared between two atoms, a(n) ________ occurs. A) polar covalent bond B) single covalent bond C) double covalent bond D) triple covalent bond E) hydrogen bond 20) ______ 21) Elements that have atoms with full outer shells of electrons A) frequently form hydrogen bonds. B) will normally form anions. C) will form many compounds. D) will normally form cations. E) are inert gases. 21) ______ 22) When atoms complete their outer electron shell by sharing electrons, they form A) cations. B) ionic bonds. C) anions. D) covalent bonds. E) hydrogen bonds. 22) ______ 23) Which of the following is not a cation? A) Mg2+ B) Na+ C) K+ D) Cl- 23) ______ E) Ca2+ 24) The weakest bond between two atoms is the ________ bond. A) polar B) ionic C) nonpolar D) hydrogen E) covalent 24) ______ 25) Ionic bonds are formed when A) two or more atoms lose electrons at the same time. B) hydrogen forms bonds with negatively charged atoms. C) electrons are completely transferred from one atom to another. D) a pair of electrons is shared unequally by two atoms. E) atoms share electrons. 25) ______ 26) In an aqueous solution, cations are attracted toward A) anions. B) water. C) salt. D) buffers. E) hydrogen ions. 26) ______ 27) Identify which of the following is both an anion and a compound: A) NaCl B) ClC) Na+ D) HCO3- 27) ______ E) K+ 28) In an aqueous solution, sodium ions would move toward A) a positive terminal. B) the bottom. C) a pH terminal. D) an organic terminal. E) a negative terminal. 28) ______ 29) When electrons are transferred from one atom to another, and the two atoms unite as a result of the opposite charges, A) an ion is formed. B) a molecule is formed. C) a covalent bond is formed. D) a hydrogen bond is formed. E) an ionic bond is formed. 29) ______ 30) Magnesium atoms have two electrons in the outermost shell. As a result, you would expect magnesium to form ions with a charge of A) -1. B) +1. C) -2. D) +2. E) either +2 or -2 30) ______ 31) Which of the following statements about hydrogen bonds is false? A) Hydrogen bonds are strong attractive forces between hydrogen atoms and negatively charged atoms. B) Hydrogen bonds are responsible for many of the properties of water. C) Hydrogen bonds can form between neighboring molecules. D) Hydrogen bonds are important for holding large molecules together. E) Hydrogen bonds can occur within a single molecule. 31) ______ 32) AB → A + B is to decomposition as A + B → AB is to A) exchange. B) metabolism. C) synthesis. D) combustion. E) replacement. 32) ______ 33) The reaction N2 + 3 H2 → 2 NH3 is an example of a(n) 33) ______ A) B) C) D) E) synthesis reaction. metabolic reaction. enzyme reaction. decomposition reaction. exchange reaction. 34) The reaction A + B + energy → AB is an example of a(n) A) decomposition reaction. B) endergonic reaction. C) exergonic reaction. D) exchange reaction. E) equilibrium reaction. 34) ______ 35) Chemical reactions that yield energy, such as heat, are said to be A) activated. B) neutral. C) exergonic. D) endergonic. E) thermonuclear. 35) ______ 36) In hydrolysis reactions, compounds react with A) water, causing decomposition. B) carbon, causing decomposition. C) glucose, causing decomposition. D) water, causing synthesis. E) hydrogen, causing decomposition. 36) ______ 37) In dehydration reactions, compounds A) convert hydrogen and oxygen to water. B) lose water molecules. C) convert water molecules to hydrogen and oxygen. D) gain electrons. E) gain water molecules. 37) ______ 38) Which one of the following statements is not correct about the reaction H2 + Cl2 → 2 HCl? 38) ______ A) B) C) D) Two molecules of HCl are formed in the reaction. One molecule of hydrogen contains two atoms. HCl is the product. H2 and Cl2 are the reactants. E) This reaction is easily reversible. 39) The molecule NO is known as A) noxious oxide. B) nitrous oxide. C) nitric oxygen. D) nitric oxide. E) noxious oxygen. 39) ______ 40) The molecule CO2 is known as 40) ______ A) B) C) D) E) carbon dioxide. carbonized oxygen. carbonated oxygen. carbon oxide. carbon monoxide. 41) The molecule H2 is known as A) B) C) D) E) helium. hydrogen. semi-water. hydrohydrogen. hydroxide. 42) The molecule O2 is known as A) B) C) D) E) 41) ______ 42) ______ oxygen. organic. oxide. B or C none of the above 43) H2O is an example of a(n) A) glucose molecule. B) molecular formula. C) ionic formula. D) covalent formula. E) water molecule. 43) ______ 44) Magnesium atoms have two electrons in the outermost shell and chlorine atoms have seven. The compound magnesium chloride would contain A) 1 magnesium and 2 chlorine. B) 2 magnesium and 1 chlorine. C) 1 magnesium and 1 chlorine. D) 2 magnesium and 7 chlorine. E) impossible to tell without more information 44) ______ 45) In the reaction listed below, what coefficient needs to be added to balance the equation? 6 CO2 + 6 H2O → C6H12O6 + ________ O2 45) ______ A) 2 B) 4 C) 6 D) 8 E) 10 46) All of the following are true concerning enzymes, except that they A) are proteins. B) function as biological catalysts. C) are consumed during the reaction. D) affect only the rate of a chemical reaction. E) lower the activation energy required for a reaction. 46) ______ 47) Substrate molecules bind to enzymes at the ________ sites. A) carboxyl B) reactant C) active D) neutral E) amino 47) ______ 48) The term ________ means each enzyme catalyzes only one type of reaction. A) monoreactive B) specificity C) saturation D) inertia E) activation 48) ______ 49) The maximum rate of an enzyme reaction occurs at A) hydrolysis. B) dehydration. C) synthesis. D) saturation limit. E) reversible. 49) ______ 50) How would the lack of a cofactor for an enzyme affect that enzyme's function? A) The enzyme would function more slowly. B) The enzyme's function would not be altered. C) The enzyme would function more quickly. D) The enzyme would cease to function after reaching a maximum rate. E) The enzyme would not be able to function. 50) ______ 51) Compounds that can be synthesized or broken down by chemical reactions inside 51) the body are called A) B) C) D) E) ___ ___ nutrients. inorganic compounds. enzymes. organic compounds. metabolites. 52) Each of the following is an example of an inorganic compound, except A) acids. B) bases. C) rocks. D) water. E) salts. 52) ______ 53) Carbohydrates, lipids, and proteins are classified as A) inorganic molecules. B) acids. C) salts. D) organic molecules. E) bases. 53) ______ 54) An example of an organic substance is A) sodium chloride. B) nitric oxide. C) oxygen. D) carbonic acid. E) sucrose. 54) ______ 55) An example of an inorganic substance is A) fructose. B) water. C) glycerol. D) carbon dioxide. E) both B and D 55) ______ 56) Which of the following statements about water is not correct? A) has a relatively low heat capacity B) is responsible for much of the mass of the human body C) contains hydrogen bonds D) can dissolve many substances E) is composed of polar molecules 56) ______ 57) During ionization, water molecules disrupt the ionic bonds of a salt to produce a mixture of ions. These ions can carry a current and so are called A) counterions. B) cations. C) acids. D) electrolytes. 57) ______ E) anions. 58) Oppositely charged ions in solution are prevented from combining by A) hydrogen bonding. B) water's nonpolar nature. C) free radicals. D) hydration spheres. E) heat capacity of water. 58) ______ 59) Which property of water helps keep body temperature stabilized? A) kinetic energy B) reactivity C) lubrication D) thermal inertia E) surface tension 59) ______ 60) Hydrophilic molecules readily associate with A) lipid molecules. B) water molecules. C) hydrophobic molecules. D) both A and B E) all of the above 60) ______ 61) A dust particle floating on a water surface illustrates A) hydrophilic attraction. B) heat capacity. C) static electricity. D) chemical tension. E) surface tension. 61) ______ 62) Nonpolar organic molecules are good examples of A) hydrophobic compounds. B) molecules that will dissociate when placed into water. C) solutes. D) hydrophilic compounds. E) electrolytes. 62) ______ 63) A solution containing equal numbers of hydrogen ions and hydroxide ions is A) in equilibrium. B) basic. C) alkaline. D) acidic. E) neutral. 63) ______ 64) Which of the following substances would be most acidic? A) urine, pH = 6 B) tomato juice, pH = 4 C) white wine, pH = 3 D) lemon juice, pH = 2 E) stomach secretions, pH = 1 64) ______ 65) If a substance has a pH that is greater than 7, it is A) neutral. B) alkaline. C) acidic. D) a salt. E) a buffer. 65) ______ 66) A(n) ________ removes hydrogen ions and a(n) ________ releases hydrogen ions. A) molecule; acid B) acid; base C) compound; element D) element; compound E) base; acid 66) ______ 67) Of the following choices, the pH of the least acidic solution is A) 6.0. B) 4.5. C) 2.3. D) 12.0. E) 1.0. 67) ______ 68) Which has the greater concentration of hydrogen ions, a substance with a pH of 5 or a substance with a pH of 4? A) A pH of 4 is greater. B) A pH of 5 is greater. C) They are both equal; 4 and 5 are relative values. D) pH 9, if you mixed the solutions . E) Not enough information to say. 68) ______ 69) Of the list below, which has the highest concentration of hydroxide ions? A) pH 14 B) pH 7 C) pH 10 D) pH 2 E) pH 1 69) ______ 70) Which pH is closest to normal body pH? A) pH 3 B) pH 2 C) pH 8 D) pH 4 E) pH 7 70) ______ 71) An excess of hydrogen ions in the body fluids can have fatal results because this can A) change the shape of large complex molecules, rendering them nonfunctional. B) disrupt tissue functions. C) block ion movements. D) all of the above 71) ______ E) A and C only 72) When placed in water, an inorganic compound dissociates 99 percent, forming hydrogen ions and anions. This compound would be A) a weak base. B) a salt. C) a strong base. D) a weak acid. E) a strong acid. 72) ______ 73) When a small amount of HCl or NaOH is added to a solution of Na2HPO4, the pH of the solution barely changes. Based on these 73) ______ observations, all of the following are true concerning the compound Na2HPO4, except A) Na2HPO4 acts as a buffer. B) Na2HPO4 is able to accept extra hydrogen ions from the HCl. C) Na2HPO4 is able to donate hydrogen ions to the OH- from NaOH. D) Na2HPO4 adsorbs excess H+ and OH- directly onto the surface of its crystalline structure. E) Na2HPO4 is a salt formed from reacting a strong base with a weak acid. 74) An important buffer in body fluids is A) NaOH. B) HCl. C) NaCl. D) H2O. 74) ______ E) NaHCO3. 75) In the body, inorganic compounds A) can serve as buffers. B) are structural components of cells. C) may be held together by ionic bonds. D) can make up proteins. E) both A and C 75) ______ 76) Oxygen is required in biological systems for A) chemical messengers. B) serving as structural components of bone. C) storage of energy. D) cellular metabolism. E) serving as catalysts. 76) ______ 77) Carbohydrate molecules A) form the regulatory molecules known as enzymes. B) are composed of C, H, O, and N atoms. C) are the building blocks of cellular membranes. D) contain the genetic information found in cells. E) are the body's most readily available source of energy. 77) ______ 78) The most important metabolic fuel molecule in the body is 78) ______ A) B) C) D) E) glucose. caffeine. sucrose. protein. vitamins. 79) Molecules that have the same molecular formula but different structural formulas are called A) isotypes. B) isomers. C) isotopes. D) isozymes. E) isomoles. 79) ______ 80) A polysaccharide that is formed in liver and muscle cells to store glucose is A) sucrose. B) cellulose. C) lactose. D) fructose. E) glycogen. 80) ______ 81) The group of organic compounds containing carbon, hydrogen, and oxygen in a near 1:2:1 ratio is defined as a A) carbohydrate. B) lipid. C) nucleic acid. D) protein. E) either A or B 81) ______ 82) Artificial sweeteners A) are generally many times sweeter than sucrose. B) provide the same number of calories as an equivalent amount of sucrose. C) are naturally similar to sugars. D) are always some form of carbohydrate. E) are inorganic sugar substitutes. 82) ______ 83) Fructose A) is an isomer of glucose. B) is a hexose. C) is found in male reproductive fluids. D) all of the above E) A and B only 83) ______ 84) When two monosaccharides undergo a dehydration synthesis, A) a disaccharide is formed. B) hydrolysis occurs. C) a starch is formed. D) a polysaccharide is formed. E) two new monosaccharides are formed. 84) ______ 85) Lipids A) help to maintain body temperature. B) provide roughly twice the energy as carbohydrates. C) form essential structural components of cells. D) cushion organs against shocks. E) all of the above 85) ______ 86) A fatty acid that contains two or more double covalent bonds is said to be A) hydrogenated. B) saturated. C) polyunsaturated. D) carboxylated. E) monounsaturated. 86) ______ 87) Most of the fat found in the human body is in the form of A) cholesterol. B) triglycerides. C) monoglycerides. D) prostaglandins. E) phospholipids. 87) ______ 88) Lipids that are produced by nearly every tissue in the body and that act as local regulators of metabolism are the A) monoglycerides. B) prostaglandins. C) glycolipids. D) steroids. E) phospholipids. 88) ______ 89) Cholesterol, phospholipids, and glycolipids are examples of A) dietary fats. B) lipid drugs. C) steroids. D) prostaglandins. E) structural lipids. 89) ______ 90) Which of the following is/are needed to form a triglyceride molecule? A) 3 fatty acid molecules B) 3 glycerol molecules C) 1 glycerol molecule D) both A and C E) both B and C 90) ______ 91) A shortage of cholesterol in the body could interfere with the formation of A) plasma membranes. B) sex hormones. C) glycogen. D) proteins. E) both A and C 91) ______ 92) You would expect a peptide bond to link A) two amino acids. B) two simple sugars. C) a sugar and a peptide. D) a peptide and a fatty acid. E) two nucleotides. 92) ______ 93) Each amino acid differs from another in the A) nature of the side chain. B) number of central carbon atoms. C) size of the amino group. D) number of peptide bonds in the molecule. E) number of carboxyl groups. 93) ______ 94) The alpha-helix and pleated sheet are examples of ________ protein structure. A) quaternary B) primary C) tertiary D) secondary E) pentanary 94) ______ 95) Interaction between individual polypeptide chains to form a protein complex is ________ structure. A) primary B) quaternary C) tertiary D) secondary E) pentagonal 95) ______ 96) Glycoproteins and proteoglycans are combinations of amino acids and A) carbohydrates. B) lipids. C) nucleic acids. D) fatty acids. E) none of the above 96) ______ 97) Which of the following is the symbol for an amino group? A) –OH B) –COOH C) –AMO D) –PO3 97) ______ E) –NH2 98) A functional group is best described as reoccurring clusters of A) atoms that greatly influence the chemical properties of molecules they are part of. B) elements that form at high pH. C) amino acids in a globular protein. D) elements that occur in a salt. E) atoms that function in the body. 98) ______ 99) A side chain on an amino acid is sometimes called ________. A) fibrous or globular. B) an isozyme. C) nucleic acid. D) an R group. E) a polypeptide chain. 99) ______ 100) Molecules that store and process genetic information are the A) lipids. B) steroids. C) nucleic acids. D) carbohydrates. E) proteins. 100) _____ 101) According to the rules of complementary base pairing in nucleic acids, cytosine would pair with the base A) uracil. B) cytosine. C) thymine. D) adenine. E) guanine. 101) _____ 102) A nucleotide consists of A) a five-carbon sugar and a nitrogenous base. B) a five-carbon sugar, a nitrogenous base, and a phosphate group. C) a five-carbon sugar and an amino acid. D) a phosphate group and a nitrogenous base. E) a five-carbon sugar and phosphate group. 102) _____ 103) Adenine and guanine are A) nucleotides represented by A and G. B) purines represented by T and C. C) pyrimidines represented by A and G. D) pyrimidines represented by T and C. E) purines represented by A and G. 103) _____ 104) An amino acid is to a protein as ________ is to a nucleic acid. A) a nucleotide B) a neutron C) a purine D) a proton E) a protein 104) _____ 105) The structure of RNA differs from DNA in that A) RNA contains purines but not pyrimidines. B) the backbone of RNA contains ribose. C) DNA contains purines but not pyrimidines. D) DNA contains pyrimidines but not purines. E) RNA contains pyrimidines but not purines. 105) _____ 106) The most abundant high-energy compound in cells is A) DNA. 106) _____ B) C) D) E) adenosine monophosphate. adenosine triphosphate. adenosine diphosphate. RNA. 107) A high-energy bond in ATP is present A) between adenine and ribose. B) between adenine and a phosphate group. C) between the first and second phosphate group. D) between the second and third phosphate group. E) both C and D 107) _____ 108) AMP + P → A) DNA B) adenine C) ATP D) 2ADP E) ADP 108) _____ 109) Identify the product formed from the phosphorylation of ADP. A) adenosine diphosphate B) ribose C) adenosine triphosphate D) deoxyribonucleic acid E) adenine 109) _____ 110) The phosphorylation of adenosine forms A) ATP. B) ADP. C) ribose. D) AMP. E) 2ATP. 110) _____ 111) The average time between synthesis and breakdown is known as the ________ time. A) catabolism B) specificity C) turnover D) anabolism E) metabolism 111) _____ 112) Continuous breakdown and replacement of cellular molecules is termed A) catabolic turnover. B) anabolic turnover. C) metabolic turnover. D) metabolism. E) both A and C 112) _____ 113) Muscle proteins are destroyed after 17 days and then replaced. This is an example of A) surface tension. B) specificity. 113) _____ C) metabolic turnover. D) surveillance. E) disease. SHORT ANSWER. Write the word or phrase that best completes each statement or answers the question. 114) A(n) _________________________ is a pure substance composed 114) ____________ of atoms. 115) The center of an atom is called the _________________________. 115) ____________ 116) Electrons whirl around the center of the atom at high speed, forming a(n) _________________________. 116) ____________ 117) Electrons in an atom occupy an orderly series of electron shells or _________________________. 117) ____________ 118) The actual mass of an atom is known as its _________________________. 118) ____________ 119) Atoms of the same element whose nuclei contain the same number of protons, but different numbers of neutrons, are called _________________________. 119) ____________ 120) The _________________________ of a radioactive substance is the time required for a 50 percent reduction in the rate of radiation emission. 120) ____________ 121) Ions with a positive charge are called _________________________. 121) ____________ 122) Ions with a negative charge are called _________________________. 122) ____________ 123) The three familiar states of matter are solids, liquids, and _________________________. 123) ____________ 124) Chemical reactions that release energy are called _________________________. 124) ____________ 125) Chemical reactions that absorb energy are called _________________________. 125) ____________ 126) Kinetic energy is stored as _________________________ energy when a spring is stretched. 126) ____________ 127) _________________________ accelerate chemical reactions that occur in the human body. 127) ____________ 128) In living cells, complex metabolic reactions proceed in a series of steps called a(n) _________________________. 128) ____________ 129) _________________________ molecules are compounds that contain carbon as the primary structural atom. 129) ____________ 130) _________________________ compounds do not usually contain carbon as a primary structural atom. 130) ____________ 131) A(n) _________________________ is a homogeneous mixture containing a solvent and a solute. 131) ____________ 132) _________________________ are soluble inorganic compounds whose solutions will conduct an electric current. 132) ____________ 133) Molecules that do not readily dissolve in water are called _________________________. 133) ____________ 134) The _________________________ of a solution is the negative logarithm of the hydrogen ion concentration expressed in moles per liter. 134) ____________ 135) All fatty acids contain a functional group at one end called the _________________________. 135) ____________ 136) In water, fatty acids tend to form tiny droplets with hydrophobic tails buried inside called _________________________. 136) ____________ 137) _________________________ are molecules with two fatty acid chains and a phosphate group that form biological membranes. 137) ____________ 138) Individual steroids differ in the _________________________ attached to the carbon rings. 138) ____________ 139) The molecule DNA contains a five-carbon sugar called _________________________. 139) ____________ 140) The purines found in DNA are _________________________ and _________________________. 140) ____________ 141) The pyrimidine bases found in DNA are _________________________ and _________________________. 141) ____________ 142) Identify the three structural components of a nucleotide. 142) ____________ 143) A(n) _________________________ is a covalent bond that stores an unusually large amount of energy. 143) ____________ 144) In the process of _________________________ a phosphate group is transferred to a molecule. 144) ____________ 145) The hydrolysis of ATP yields ADP, phosphate ion, and _________________________. 145) ____________ ESSAY. Write your answer in the space provided or on a separate sheet of paper. 146) The element sulfur has an atomic number of 16 and mass number of 32. How many neutrons are in the nucleus of a sulfur atom? If sulfur forms covalent bonds with hydrogen, how many hydrogen atoms can bond to one sulfur atom? 147) What role do buffer systems play in the human body? 148) Blood has a very narrow normal pH range but urine has a very broad normal pH range. What does that indicate about the physiology of pH? 149) Explain the role of water molecules in polysaccharide formation. 150) How does the DNA molecule control the appearance and function of a cell? 1) 2) 3) 4) 5) 6) 7) 8) 9) 10) 11) 12) 13) 14) 15) 16) 17) 18) 19) 20) 21) 22) 23) 24) 25) 26) 27) 28) 29) 30) 31) 32) 33) 34) 35) 36) 37) 38) 39) 40) 41) 42) 43) 44) 45) 46) 47) 48) 49) 50) 51) E B E E C B A D C A A A E B A C D E C A E D D D C A D E E D A C A B C A B E D A B A B A C C C B D E E 52) 53) 54) 55) 56) 57) 58) 59) 60) 61) 62) 63) 64) 65) 66) 67) 68) 69) 70) 71) 72) 73) 74) 75) 76) 77) 78) 79) 80) 81) 82) 83) 84) 85) 86) 87) 88) 89) 90) 91) 92) 93) 94) 95) 96) 97) 98) 99) 100) 101) 102) 103) C D E E A D D D B E A E E B E D A A E D E D E E D E A B E A A D A E C B B E E E A A D B A E A D C E B E 104) 105) 106) 107) 108) 109) 110) 111) 112) 113) 114) 115) 116) 117) 118) 119) 120) 121) 122) 123) 124) 125) 126) 127) 128) 129) 130) 131) 132) 133) 134) 135) 136) 137) 138) 139) 140) 141) 142) 143) 144) 145) 146) A B C E E C D C C C element nucleus electron cloud energy levels atomic weight isotopes half-life cations anions gases exergonic endergonic potential Enzymes pathway Organic Inorganic solution Electrolytes hydrophobic pH carboxylic acid group micelles Phospholipids side chains deoxyribose adenine; guanine thymine; cytosine pentose; phosphate group; nitrogenous base high-energy bond phosphorylation energy The number of neutrons in an atom is equal to the mass number minus the atomic number. Thus, sulfur has 32 — 16 = 16 neutrons. The atomic number indicates the number of protons, so a neutral sulfur atom contains 16 protons plus 16 electrons to balance the protons electrically. The electrons would be distributed as follows: 2 in the first electron shell, 8 in the second, and the remaining 6 in the third. To achieve a full 8 electrons in the third (outermost) electron shell, the sulfur atom can accept 2 electrons in an ionic bond or can share 2 electrons in a covalent bond. Because hydrogen atoms can share one electron in a covalent bond, the sulfur atom can form two covalent bonds with hydrogen, one with each of two hydrogen atoms. In chemical notation, this is H 2S. 147) Buffer systems help maintain pH within normal limits by removing or replacing hydrogen ions as needed. 148) Homeostasis requires that the pH of body fluids be maintained almost constant to avoid disruptions of healthy function. To accomplish this, the urinary system eliminates or retains hydrogen ion as needed. These actions cause the pH of urine to vary widely, depending on whether there is too much or not enough hydrogen ion in the body. 149) Water molecules are removed in the dehydration synthesis of polysaccharides. 150) The DNA molecule controls the synthesis of enzymes and structural proteins. By controlling the synthesis of structural proteins, the DNA is able to influence the physical appearance of a cell. By controlling the production of enzymes, the DNA is able to control all aspects of cellular metabolism and thus control the activity and biological functions of the cell.